1. Field of the Invention
This invention relates to a rubber plug used in a connector required to have a waterproof effect, and also to a withdrawal prevention structure for preventing the rubber plug from being easily disengaged from a metal terminal.
2. Conventional Art of the Invention
A conventional rubber plug of this type is shown in FIG. 1. As shown in this Figure, the rubber plug 40 is fitted on a front end portion of a sheath of a wire 41, and is fixedly clamped to the wire by a metal terminal 42, and in this condition the rubber plug is inserted into a cavity in a connector housing. The rubber plug 40 has a cylindrical shape as a whole, and has a wire insertion hole 43 extending therethrough along an axis thereof, and the wire 41 can be passed through this hole 43 in a sealed manner. Two annular seal lips 44 are formed on an outer peripheral surface of the rubber plug 40 at a rear portion thereof, and a clamping region 46 to be clamped by an insulation barrel 45 of the metal terminal 42 is provided at a front end portion of the rubber plug.
The force of clamping between the rubber plug 40 and the metal terminal 42 is provided by a clamping force applied by the insulation barrel 45, and therefore the withdrawal of the rubber plug 40 can be prevented merely by increasing the clamping force. However, if the clamping force is merely increased, end edges of the insulation barrel 45 bite the rubber plug 50 to such an extent that the rubber plug 40 may be damaged if the end edge of the insulation barrel 45 is formed into a sharp edge. In such a case, the sealing property would be adversely affected. Therefore, it is not proper to merely increase the clamping force. Despite this, the above type is not provided with any withdrawal prevention means, and therefore is not satisfactory from the viewpoint of withdrawal prevention.
To deal with this problem, there has been developed a rubber plug 30 shown in FIG. 2. This rubber plug 30 includes a waterproof portion 31 and a clamping portion 32, and has a tubular shape as a whole, the rubber plug 30 having an insertion hole 33 formed therethrough along its axis for passing a wire W therethrough. Two ribs 34 are formed on an outer peripheral surface of the waterproof portion 31, and can be elastically deformed into intimate contact with an inner peripheral surface of a cavity (not shown), thereby preventing water from introducing into the cavity. A metal terminal T shown in FIG. 4 is attached to the clamping portion 32, and the clamping portion 32 is smaller in outer diameter than the waterproof portion 31. A barrel B, formed at a rear end of the metal terminal T, is compressively clamped to the outer periphery of the clamping portion 32. When the barrel B is thus clamped to the clamping portion 32, the metal terminal is disposed at a right side (FIG. 2) of the rubber plug 30, and the wire W, fixedly connected to the rear end portion of the metal terminal, passes through the insertion hole 33, and extends outwardly from the rubber plug 30 left (FIG. 2).
A flange-like withdrawal prevention portion 35 is formed on a distal end (right end in FIG. 2) of the clamping portion 32 remote from the waterproof portion 31 over an entire periphery thereof. This withdrawal prevention portion 35 serves to prevent the barrel B from being disengaged from the clamping portion 32 when inserting the rubber plug 30, together with the metal terminal, into the cavity.
When the rubber plug 30 of the above construction is to be inserted into the cavity, the metal terminal mounted on the right side (FIG. 2) of the rubber plug 30 is directed toward the cavity, and then the rubber plug is inserted, together with the metal terminal, into the cavity. This inserting operation is carried out by first holding the rubber plug 30 by the fingers and by pushing the rear end of the rubber plug. If it is necessary to insert the rubber plug 30 to a deeper position in the cavity even after the rubber plug 30 is fully received in the cavity, the exposed portion of the wire W, extending outwardly from the rubber plug 30 and disposed outwardly of the cavity, is held by the fingers, and is pushed toward the cavity.
At this time, the wire W is advanced, together with the metal terminal, into a deeper position in the cavity whereas the rubber plug 30 can not advance easily because of a frictional resistance between the rubber plug and an inner surface of the cavity. Therefore, there is a fear that the barrel B tends to be displaced relative to the clamping portion 32 toward the front end (right end in FIG. 2) of the rubber plug. The barrel B, if thus displaced toward the front end, abuts the withdrawal prevention portion 35 (see FIG. 3), and therefore is prevented from further displacement, thereby preventing the barrel B from being disengaged from the clamping portion 32. Thereafter, the rubber plug 30 and the metal terminal, held in a condition shown in FIG. 3, are inserted in unison in the cavity.
Furthermore, there has been proposed a rubber plug 50 in Japanese Utility Model Unexamined Publication No. 62-163879 as shown in FIG. 5. In this rubber plug 50, an annular projection 52 is formed on a surface of a wire insertion hole 51 at a front end thereof, so that the inner diameter of the wire insertion hole 51 is made smaller at the projection 52 than the outer diameter of a wire 53 to be inserted into the insertion hole 51. With this arrangement, a front end of the rubber plug 50 is forcibly bulged when the wire 53 is passed therethrough, and this bulged end is engaged with an insulation barrel as shown in FIG. 6. As a result, the rubber plug 50 is prevented from withdrawal.
However, in the structure shown in FIG. 2 in which the withdrawal prevention portion 35 is merely provided in a projected manner, when the frictional resistance between the rubber plug 30 and the inner surface of the cavity becomes so large that a pressing force acting from the barrel B on the withdrawal prevention portion 35 exceeds a limit value, the barrel B elastically deforms and bends the withdrawal prevention portion 35 right (FIG. 3). At the same time, the barrel B gradually squeezes the withdrawal prevention portion 30 to pass past the same. As a result, in some cases, the barrel B has been disengaged from the clamping portion 32, thus losing the function of retaining the barrel B.
Furthermore, the rubber plug structure shown in FIG. 5 has the following problem to be solved. Because of the provision of the annular projection on the surface of the wire insertion hole, the inner diameter of the wire insertion hole is constricted, so that the wire can not be easily passed therethrough. Therefore, the wire insertion operation is rather troublesome, and can not be carried out efficiently.
The rubber plug must also meet the sealing requirement. For example, in the rubber plug 40 shown in FIG. 1, sealing engagement of the rubber plug 40 with the housing is achieved by the seal lips 44, and the plug 31 also have inner lips 47 for sealing contact with the wire. Even in the type of rubber plug having such inner lips 37, if the wire 41 is pulled, a gap develops between the inner surface of the wire insertion hole 43 and the wire 41, thus adversely affecting the sealing property.